fix(config): apply env overrides at runtime and fix Docker compose defaults (#279)

- Call apply_env_overrides() after Config::load_or_init() in main.rs so
  environment variables (API_KEY, PROVIDER, ZEROCLAW_GATEWAY_PORT, etc.)
  are actually applied at runtime, not just in tests
- Add ZEROCLAW_ALLOW_PUBLIC_BIND env var support for gateway bind policy
- Fix docker-compose.yml: correct volume path (/zeroclaw-data not /data),
  add ZEROCLAW_ALLOW_PUBLIC_BIND=true for container networking, make host
  port configurable via HOST_PORT env var
- Add docker-compose.override.yml to .gitignore for local dev overrides

src/config/schema.rs

@@ -1002,6 +1002,11 @@ impl Config {
             }
         }
 
+        // Allow public bind: ZEROCLAW_ALLOW_PUBLIC_BIND
+        if let Ok(val) = std::env::var("ZEROCLAW_ALLOW_PUBLIC_BIND") {
+            self.gateway.allow_public_bind = val == "1" || val.eq_ignore_ascii_case("true");
+        }
+
         // Temperature: ZEROCLAW_TEMPERATURE
         if let Ok(temp_str) = std::env::var("ZEROCLAW_TEMPERATURE") {
             if let Ok(temp) = temp_str.parse::<f64>() {